Abstract: Based on the operation characteristics of the nuclear power unit,the radioactive inventory of activated parts was calculated by ORIGEN2,and the effects of burn-up,operation mode and power change on the radioactive inventory for activated parts were analyzed.The results indicated that the radioactive inventory grew with the increasing of burn-up,and when the actual operation time was longer than the effective operation time,the increasing rate of nuclide activity approximated the burn-up increasing;Radioactive inventory of activated parts was influenced directly by the operation modes of the nuclear power unit,and under same reactor load,operation power and burn-up,the radioactive inventory for non-continuous operation mode is less than that for the continuous operation mode.Effects of operation modes on radioactive inventory reversed with half life of nuclides.Under same burn-up and longer operation time,the effect of operation power change on the radioactive inventory is not obvious.